What Causes Nausea With Pain In Sternum?

Hi. I just had some roast beef on bread with mayonnaise-based horseradish sauce. About 30 minutes after, I started having nausea and some pain. The pain was about a 1 to 1.5 and located directly below (as in floor direction) my sternum. I also had a little pain in my back like a slight burning. It's starting to go away now, but I still have a slight bit of nausea and it feels like there's a slight "lump in my throat." I took some omeprozole to help and it seems to have had some effect. Could this be my gall bladder? I have been having this same thing happen on and off for about 3 or four months now. And last time I went to the ER (about a month ago), they did an ultrasound on my gall bladder and had said I do have a stone.